A wireless power transmission or a wireless energy transfer refers to a technology for wirelessly transferring electric energy to desired devices. In the 1800's, an electric motor or a transformer employing the principle of electromagnetic induction has been extensively used and then a method for transmitting electric energy by irradiating electromagnetic waves, such as radio waves or lasers, has been suggested. Actually, electric toothbrushes or electric razors, which are frequently used in daily life, are charged based on the principle of electromagnetic induction. Until now, the long-distance transmission using the magnetic induction, the resonance and the short-wavelength radio frequency has been used as the wireless energy transfer scheme.
A plurality of coils are used for the wireless power transmission. For instance, litz coils are mainly used for the wireless power transmission. The litz coil consists of a plurality of wires and the spark may occur due to potential difference between the wires if one of the wires is open.